ADVANCED MODES OF MECHANICAL VENTILATION

ADVANCED MODES OF
MECHANICAL VENTILATION
Mazen Kherallah, MD, FCCP
POINTS OF DISCUSSION
|
Triggered Modes of Ventilation
Volume Support (VS)
y Proportional Assist Ventilation (PAV or PPS)
y
|
Hybrid Modes of Ventilation
y
y
y
y
y
y
Volume Assured Pressure Support
Pressure Regulated Volume Control (PRVC)
Auto mode: VS and PRVC
Adaptive Support Ventilation: ASV
Bi-level Ventilation (APRV and Bi-vent)
Mandatory Minute Ventilation (MMV)
NEW MODES OF VENTILATION
DUAL-CONTROLLED MODES
Type
Manufacturer;
ventilator
Name
Dual control within a breath
VIASYS Healthcare; Bird
8400Sti and Tbird
VIASYS Healthcare; Bear 1000
Volume-assured pressure
support
Pressure augmentation
Dual control breath to breath:
Pressure-limited flow-cycled
ventilation
Siemens; servo 300
Cardiopulmonary corporation;
Venturi
Volume support
Variable pressure support
Dual control breath to breath:
Pressure-limited time-cycled
ventilation
Siemens; servo 300
Pressure-regulated volume
control
Adaptive pressure ventilation
Autoflow
Variable pressure control
Dual control breath to breath:
SIMV
Hamilton; Galileo
Hamilton; Galileo
Drager; Evita 4
Cardiopulmonary corporation;
Venturi
Adaptive support ventilation
DUAL CONTROL BREATH-TO-BREATH
PRESSURE-LIMITED FLOW-CYCLED VENTILATION
VOLUME SUPPORT
Control Trigger
Pressure
Patient
Limit
Target
Cycle
Pressure
Volume
Flow
Pressure Limited Flow Cycled Ventilation
VS (VOLUME SUPPORT)
Apnea
Upper Pressure limit
Pressure
5 cm H2O
5 cm H2O
1
2
3
4
6
5
Flow
Constant exp. Flow
(1), VS test breath (5 cm H2O); (2), pressure is increased slowly until target volume is achieved; (3),
maximum available pressure is 5 cm H2O below upper pressure limit; (4), VT higher than set VT
delivered results in lower pressure; (5), patient can trigger breath; (6) if apnea alarm is detected,
ventilator switches to PRVC
yes
Calculate new
Pressure limit
Trigger
no
Pressure limit
Based on VT/C
Volume from
Ventilator=
Set tidal volume
Flow= 5% of
Peak flow
Calculate
compliance
yes
no
Control logic for volume support mode of the servo 300
Cycle off
DUAL CONTROL BREATH TO BREATH:
PROPORTIONAL ASSIST VENTILATION(PAS)/PROPORTIONAL PRESSURE SUPPORT (PPS)
Control Trigger
Pressure
Patient
Limit
Target
Cycle
Pressure
Volume
Flow
Pressure Limited Flow Cycled Ventilation
PROPORTIONAL ASSIST VENTILATION
(PAV)
Changing pressure support based on patient’s efforts
Pressure
Flow
Time
Time
Rregulates the pressure output of the ventilator moment by moment in
accord with the patient’s demands for flow and volume.
Thus, when the patient wants more, (s)he gets more help; when less, (s)he
gets less. The timing and power synchrony are therefore nearly optimal—at
least in concept.
PROPORTIONAL ASSIST AMPLIFIES
MUSCULAR EFFORT
Muscular effort (Pmus) and
airway pressure assistance
(Paw) are better matched
for Proportional Assist
(PAV) than for Pressure
Support (PSV).
PAV (PROPORTIONAL ASSIST VENTILATION)
| Indications
Patients who have WOB
problems associated with
worsening lung
characteristics
| Asynchronous patients who
are stable and have an
inspiratory effort
| Ventilator-dependent
patients with COPD
|
PAV (PROPORTIONAL ASSIST VENTILATION)
Disadvantages
|
|
|
|
|
Patient must have an adequate
spontaneous respiratory drive
Advanyages
|
Variable VT and/or PIP
Correct determination of CL and Raw
is essential (difficult). Both under and
over estimates of CL and Raw during
ventilator setup may significantly
impair proper patient-ventilator
interaction, which may cause
excessive assist (“Runaway”) – the
pressure output from the ventilator
can exceed the pressure needed to
overcome the system impedance (CL
and Raw)
Air leak could cause excessive assist or
automatic cycling
Trigger effort may increase with autoPEEP
|
|
|
The patient controls the
ventilatory variables ( I, PIP,
TI, TE, VT)
Trends the changes of
ventilatory effort over time
When used with CPAP,
inspiratory muscle work is
near that of a normal subject
and may decrease or prevent
muscle atrophy
Lowers airway pressure
DUAL CONTROL WITHIN A BREATH
VOLUME-ASSURED PRESSURE SUPPORT
Control Trigger
Dual
Pressure/
Volume
Patient
Limit
Target
Cycle
Pressure
Volume
Flow or
volume
Volume Assured Pressure Support Ventilation
Pressure limit
overridden
40
Set pressure limit
Paw
cmH20
-20
0.6
Volume
Set tidal volume cycle threshold
Tidal volume
met
Tidal volume
not met
L
0
60
Inspiratory flow
greater than set flow
Flow cycle
Set flow
Inspiratory flow
equals set flow
Flow
L/min
60
Switch from Pressure control to
Volume/flow control
Trigger
Pressure at
Pressure support
no
flow=
25% peak
yes
yes
delivered VT
≥ set VT
no
Cycle off
inspiration
Insp flow
> Set flow
yes
no
Switch to flow control
at peak flow setting
no
yes
delivered VT
= set VT
no
PAW <PSV
setting
yes
Control logic for volume-assured pressure-support mode
DUAL CONTROL BREATH-TO-BREATH
PRESSURE REGULATED VOLUME CONTROL
Control Trigger
Volume
Patient or
Time
Limit
Target
Cycle
Pressure
Lowest
pressure
for set
volume
Time
Pressure-limited Time-cycled Ventilation
PRVC (PRESSURE REGULATED VOLUME
CONTROL)
Upper Pressure Limit
Pressure
Floe
1
5 cm H2O
2
3
4
5
6
Time
Time
PRVC. (1), Test breath (5 cm H2O); (2) pressure is increased to deliver set volume; (3), maximum
available pressure; (4), breath delivered at preset E, at preset f, and during preset TI; (5), when VT
corresponds to set value, pressure remains constant; (6), if preset volume increases, pressure
decreases; the ventilator continually monitors and adapts to the patient’s needs
PRVC AUTOMATICALLY ADJUSTS TO
COMPLIANCE CHANGES
yes
Calculate new
Pressure limit
Trigger
no
Pressure limit
Based on VT/C
Volume from
Ventilator=
Set tidal volume
Time= set
Inspiratory time
Calculate
compliance
yes
no
Control logic for pressure-regulated volume control and autoflow
Cycle off
PRVC (PRESSURE REGULATED VOLUME
CONTROL)
Disadvantages and Risks
|
|
|
|
|
Varying mean airway
pressure
May cause or worsen autoPEEP
When patient demand is
increased, pressure level may
diminish when support is
needed
May be tolerated poorly in
awake non-sedated patients
A sudden increase in
respiratory rate and demand
may result in a decrease in
ventilator support
Afvantages
|
Maintains a minimum PIP
|
Guaranteed VT
|
|
|
Patient has very little WOB
requirement
Allows patient control of
respiratory rate Decelerating
flow waveform for improved
gas distribution
Breath by breath analysis
PRVC (PRESSURE REGULATED VOLUME
CONTROL)
|
Indications
Patient who require the lowest possible pressure and a
guaranteed consistent VT
| ALI/ARDS
| Patient with the possibility of CL or Raw changes
|
AUTOMODE
Mandatory
Spontaneous
PRVC
VS
Ventilator triggered, pressure
controlled and time cycled; the
pressure is adjusted to
maintain the set tidal volume
Patient triggered, pressure
limited, and flow cycled.
Apnea for 12 seconds
Two consecutive breaths
DUAL CONTROL BREATH-TO-BREATH
ADAPTIVE SUPPORT VENTILATION
ASV (ADAPTIVE SUPPORT VENTILATION)
|
A dual control mode that uses pressure
ventilation (both PC and PSV) to maintain a set
minimum E (volume target) using the least
required settings for minimal WOB depending on
the patient’s condition and effort
y
It automatically adapts to patient demand by
increasing or decreasing support, depending on the
patient’s elastic and resistive loads
ASV (ADAPTIVE SUPPORT VENTILATION)
|
|
|
|
|
|
The clinician enters the patient’s IBW, which allows the
ventilator’s algorithm to choose a required E. The ventilator
then delivers 100 mL/min/kg.
A series of test breaths measures the system C, resistance and
auto-PEEP
If no spontaneous effort occurs, the ventilator determines the
appropriate respiratory rate, VT, and pressure limit delivered for
the mandatory breaths
I:E ratio and TI of the mandatory breaths are continually being
“optimized” by the ventilator to prevent auto-PEEP
If the patient begins having spontaneous breaths, the number of
mandatory breaths decrease and the ventilator switches to PS at
the same pressure level
Pressure limits for both mandatory and spontaneous breaths are
always being automatically adjusted to meet the E target
ASV (ADAPTIVE SUPPORT VENTILATION)
|
Indications
Full or partial ventilatory support
| Patients requiring a lowest possible PIP and a guaranteed
VT
| ALI/ARDS
| Patients not breathing spontaneously and not triggering the
ventilator
| Patient with the possibility of work land changes (CL and
Raw)
| Facilitates weaning
|
ASV (ADAPTIVE SUPPORT VENTILATION)
Disadvantages and Risks
|
|
|
|
|
Inability to recognize and
adjust to changes in alveolar
VD
Possible respiratory muscle
atrophy
Varying mean airway
pressure
In patients with COPD, a
longer TE may be required
A sudden increase in
respiratory rate and demand
may result in a decrease in
ventilator support
Advantages
|
Guaranteed VT and VR
|
Minimal patient WOB
|
|
|
|
|
Ventilator adapts to the
patient
Weaning is done
automatically and
continuously
Variable Vm to meet patient
demand
Decelerating flow waveform
for improved gas distribution
Breath by breath analysis
MMV (MANDATORY MINUTE VENTILATION)
|
|
|
AKA: Minimum Minute Ventilation or Augmented minute
ventilation
Operator sets a minimum E which usually is 70% - 90% of
patient’s current E. The ventilator provides whatever
part of the E that the patient is unable to accomplish.
This accomplished by increasing the breath rate or the
preset pressure.
It is a form of PSV where the PS level is not set, but rather
variable according to the patient’s need
MMV (MANDATORY MINUTE VENTILATION)
|
Indications
Any patient who is spontaneously and is deemed ready to
wean
| Patients with unstable ventilatory drive
|
MMV (MANDATORY MINUTE VENTILATION)
Disadvantages
|
|
|
|
|
An adequate E may not equal
sufficient A (e.g., rapid shallow
breathing)
The high rate alarm must be set
low enough to alert clinician of
rapid shallow breathing
Variable mean airway pressure
An inadequate set E
(>spontaneous E) can lead to
inadequate support and patient
fatigue
An excessive set E
(>spontaneous E) with no
spontaneous breathing can lead
to total support
Advantages
|
|
Full to partial ventilatory
support
Allows spontaneous
ventilation with safety net
|
Patient’s E remains stable
|
Prevents hypoventilation
BILEVEL VENTILATION
60
PEEPH
Paw
PEEPL
cmH20
-20
Pressure Support
PEEPHigh + PS
1
2
3
4
5
6
7
Pressure
Thigh
Phigh
Tlow
Plow
Pressure
Time
Psupp
Time
Pressure
Thigh
Phigh
Tlow
Plow
Pressure
Time
Phigh
Psupp
Time
Pressure
Thigh
Phigh
Tlow
Plow
Pressure
Time
Phigh
Psupp
Time
Psupp
AIRWAY PRESSURE RELEASE
VENTILATION
Control Trigger
Pressure
Time
Limit
Cycle
Pressure
Time
Time Triggered Time-cycled Ventilation
AIRWAY PRESSURE RELEASE
VENTILATION
Spontaneous Breaths
60
Paw
Releases
cmH20
-20
1
2
3
4
5
6
7
8
APRV (AIRWAY PRESSURE RELEASE
VENTILATION)
Spontaneous breaths
Airway Pressure
CPAP Released
CPAP Restored
CPAP Level
CPAP Level 1
CPAP Level 2
Time
APRV (AIRWAY PRESSURE
RELEASE VENTILATION)
|
Indications
y
y
y
y
y
Partial to full ventilatory support
Patients with ALI/ARDS
Patients with refractory hypoxemia
due to collapsed alveoli
Patients with massive atelectasis
May use with mild or no lung disease
APRV (AIRWAY PRESSURE RELEASE
VENTILATION)
Disadvantages and Risks
|
|
|
|
|
|
Variable VT
Could be harmful to patients
with high expiratory
resistance (i.e., COPD or
asthma)
Advantages
|
|
Auto-PEEP is usually present
Caution should be used with
hemodynamically unstable
patients
|
Asynchrony can occur is
spontaneous breaths are out
of sync with release time
|
Requires the presence of an
“active exhalation valve”
|
|
|
Allows inverse ratio ventilation
(IRV) with or without
spontaneous breathing (less need
for sedation or paralysis)
Improves patient-ventilator
synchrony if spontaneous
breathing is present
Improves mean airway pressure
Improves oxygenation by
stabilizing collapsed alveoli
Allows patients to breath
spontaneously while continuing
lung recruitment
Lowers PIP
May decrease physiologic
deadspace
QUESTIONS